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.Dd October 4, 2021
.Dt TIME.H 3HEAD
.Os
.Sh NAME
.Nm time.h ,
.Nm time
.Nd time types
.Sh SYNOPSIS
.In time.h
.Sh DESCRIPTION
The
.In time.h
header declares the structure
.Vt tm ,
which includes the following members:
.Bd -literal -offset indent
int tm_sec     /* seconds [0,60] */
int tm_min     /* minutes [0,59] */
int tm_hour    /* hour [0,23] */
int tm_mday    /* day of month [1,31] */
int tm_mon     /* month of year [0,11] */
int tm_year    /* years since 1900 */
int tm_wday    /* day of week [0,6] (Sunday =0) */
int tm_yday    /* day of year [0,365] */
int tm_isdst   /* daylight savings flag */
.Ed
.Pp
The value of
.Fa tm_isdst
is positive if Daylight Saving Time is in effect, 0 if Daylight Saving
Time is not in effect, and negative if the information is not available.
.Pp
The
.In time.h
header defines the following symbolic names:
.Bl -tag -width Ds
.It Dv CLOCK_MONOTONIC
The identifier for the system-wide monotonic clock, which is defined as a clock
whose value cannot be set with
.Fn clock_settime
and that cannot have backward clock jumps.
The maximum possible clock jump is implementation-defined.
See
.Xr clock_settime 3C .
.It Dv CLOCKS_PER_SEC
A number used to convert the value returned by the
.Fn clock
function into seconds.
See
.Xr clock 3C .
.It Dv CLOCK_PROCESS_CPUTIME_ID
The identifier of the CPU-time clock associated with the process making a
.Fn clock
or
.Fn timer_*
function call.
This clock includes both user and system CPU-time.
.It Dv CLOCK_REALTIME
The identifier of the system-wide realtime clock.
.It Dv CLOCK_THREAD_CPUTIME_ID
The identifier of the CPU-time clock associated with the thread making a
.Fn clock
or
.Fn timer_*
function call.
This clock includes both user and system CPU-time.
.It Dv CLOCK_VIRTUAL
The identifier of the CPU-time clock associated with the thread making a
.Fn clock
or
.Fn timer_*
function call.
This clock only includes user CPU-time.
.It Dv NULL
Null pointer constant.
.It Dv TIMER_ABSTIME
Flag indicating time is absolute.
For functions taking timer objects, this refers to the clock associated
with the timer.
.It Dv TIME_UTC
The identifier for the system-wide realtime clock with no time zone
translation.
Used in
.Fn timespec_get .
.El
.Pp
The
.In time.h
header declares the
.Vt timespec
structure, which has the following members:
.Bd -literal -offset indent
time_t tv_sec     /* seconds */
long   tv_nsec     /* nanoseconds */
.Ed
.Pp
The
.In time.h
header declares the
.Vt itimerspec
structure, which has the following members:
.Bd -literal -offset indent
struct timespec it_interval     /* timer period */
struct timespec it_value     /* timer expiration */
.Ed
.Pp
The
.Vt clock_t ,
.Vt size_t ,
.Vt time_t ,
.Vt clockid_t ,
and
.Vt timer_t
types are defined as described in
.In sys/types.h .
See
.Xr types.h 3HEAD .
.Pp
Although the value of
.Dv CLOCKS_PER_SEC
is required to be 1 million on all standard-conforming systems, it can
be variable on other systems, and it should not be assumed that
.Dv CLOCKS_PER_SEC
is a compile-time constant.
.Pp
The
.In time.h
header provides a declaration for
.Dv getdate_err .
.Pp
The following are declared as variables:
.Bd -literal -offset indent
extern int daylight;
extern long timezone;
extern char *tzname[];
.Ed
.Pp
Inclusion of the
.In time.h
header can make visible all symbols from the
.In signal.h
header.
.Sh USAGE
The range [0,60] for
.Fa tm_sec
allows for the occasional leap second.
.Pp
.Fa tm_year
is a signed value; therefore, years before 1900 can be represented.
.Pp
To obtain the number of clock ticks per second returned by the
.Fn times
function, applications should call
.Fn sysconf "_SC_CLK_TCK" .
See
.Xr times 2
and
.Xr sysconf 3C .
.Sh INTERFACE STABILITY
.Sy Committed
.Sh SEE ALSO
.Xr time 2 ,
.Xr utime 2 ,
.Xr clock 3C ,
.Xr clock_settime 3C ,
.Xr ctime 3C ,
.Xr difftime 3C ,
.Xr getdate 3C ,
.Xr mktime 3C ,
.Xr nanosleep 3C ,
.Xr strftime 3C ,
.Xr strptime 3C ,
.Xr timer_create 3C ,
.Xr timer_delete 3C ,
.Xr timer_settime 3C ,
.Xr timespec_get 3C ,
.Xr types.h 3HEAD ,
.Xr attributes 7 ,
.Xr standards 7
